1. Field of Invention
The present invention relates to a tire grinding method and grinding device that grind a tread portion of a tire to be retreaded in order to retread a worn tire to be retreaded.
2. Related Art
Techniques for retreading retreadable tires may be broadly classified into mold vulcanization (hot retreading), which uses a tire mold (die), and precure retreading (cold retreading), which does not use a mold but attaches a patterned tread that has already been vulcanized to a base tire and vulcanizes this in a vulcanization can. In either technique, as for the tire to be retreaded (base tire) that is supplied to retreading, first, the tread portion is cut and formed into a required shape in a buffing step, but in regard to the buffed tire after implementation of this buffing, the thickness from the embedded belt layer to the outer peripheral surface (old rubber thickness) becomes an important factor that determines the performance of the retreaded tire (particularly exothermic durability).
In Patent Document 1, there is disclosed a grinding device that can automatically control the grinding amount with respect to the base tire such that the above mentioned old rubber thickness of the base tire after grinding becomes an optimum value that has been set beforehand. In the grinding device of Patent Document 1, Japanese Patent Application Laid-Open No. 58-1546, a tire to be retreaded that is rotatably held by a holding mechanism is caused to rotate, the belt layer of the tire to be retreaded is detected by a metal sensor to measure the old rubber thickness of the tire to be retreaded, the outer peripheral surface of the tire to be retreaded is grinded by a grinding mechanism, and cutting and grinding of the tire to be retreaded by the grinding mechanism is stopped at a timing when the old rubber thickness of the tire to be retreaded becomes the optimum value.
However, in the grinding device of Patent Document 1, when the tire to be retreaded is rotated about a central axis (device axial center) of the holding mechanism and the outer peripheral surface of the tire to be retreaded is grinded by the grinding mechanism, when the device axial center and the central axis of the tire to be retreaded (tire axial center) coincide, the tire to be retreaded can be grinded such that the old rubber thickness becomes constant (the optimum value) at an arbitrary site along the tire rotational direction. However, when the device axial center and the central axis of the tire to be retreaded (tire axial center) do not coincide, the old rubber thickness along the tire rotational direction of the tire to be retreaded after grinding does not become constant, and deviation corresponding to the eccentricity amount of the tire to be retreaded arises in the old rubber thickness. For this reason, when the device axial center and the tire axial center do not coincide due to eccentricity or deformation of the tire to be retreaded, the old rubber thickness of the tire to be retreaded after grinding becomes nonuniform, performance such as durability of a retreaded tire that has been manufactured from the tire to be retreaded drops, or the old rubber thickness of the tire to be retreaded after grinding locally disappears and the belt layer becomes exposed, and there is potential to become unable to manufacture a retreaded tire from this tire to be retreaded.
In consideration of the above-described circumstances, it is an object of the present invention to provide a tire grinding method and grinding device that can grind a tire to be retreaded by grinding means such that the thickness of residual rubber on an outer peripheral side of a belt layer of the tire to be retreaded becomes constant even when eccentricity arises in the tire to be retreaded.
In order to achieve this object, a tire grinding method pertaining to a first aspect of the present invention includes: when a tire to be retreaded is loaded into a holding mechanism of a grinding device and a tread portion of the tire to be retreaded that is rotated by the holding mechanism about a device axial center is to be grinded by grinding means, detecting, with a metal detection sensor along a rotating direction whose center is the device axial center, a distance from the device axial center to a metal belt layer of the tire to be retreaded that is held by the holding mechanism, and thereafter causing the grinding means to relatively move with respect to the tire to be retreaded along a radial direction whose center is the device axial center on the basis of a position along a rotating direction of the tire to be retreaded and the detected value of the distance from the device axial center to the belt layer, and grinding, with the grinding means, the tread portion of the tire to be retreaded that is rotated by the holding mechanism.
In the tire grinding method pertaining to a first aspect, first, the distance from the device axial center to the metal belt layer of the tire to be retreaded that is rotated by the holding mechanism is detected by the metal detection sensor along the tire rotating direction, whereby the distance from the device axial center to the belt layer that corresponds to the position (phase) along the rotating direction of the tire to be retreaded can be determined as a detected value by a detection signal from the metal detection sensor, so the eccentricity amount and the eccentricity direction of the tire to be retreaded with respect to the device axial center, corresponding to the phase of the tire to be retreaded, can be respectively determined on the basis of this detected value.
In the tire grinding method pertaining to a first aspect, next, the grinding means is caused to relatively move with respect to the tire to be retreaded along the radial direction whose center is the device axial center on the basis of the phase of the tire to be retreaded and the eccentricity amount and eccentricity direction of the tire to be retreaded that have been determined as described above, and the tread portion of the tire to be retreaded that is rotated by the holding mechanism is grinded by the grinding means, whereby the tire to be retreaded can be grinded by the grinding means such that the thickness of residual rubber on the outer peripheral side of the belt layer of the tire to be retreaded becomes constant even if eccentricity with respect to the device axial center arises in the tire to be retreaded.
Further, in a tire grinding method pertaining to a second aspect in the tire grinding method of a first aspect, when the tire to be retreaded is grinded by the grinding means, the grinding means is relatively moved along the radial direction, such that a distance from a center of curvature of the belt layer of the tire to be retreaded to the grinding means becomes constant, on the basis of the position along the rotating direction of the tire to be retreaded and the detected value of the distance from the device axial center to the belt layer that has been detected by the metal detection sensor.
Further, in a tire grinding method pertaining to a third aspect in the tire grinding method of a first or second aspect, before the distance from the device axial center to the metal belt layer of the tire to be retreaded that is held by the holding mechanism is detected by the metal detection sensor along the tire rotating direction, the tread portion is grinded until groove portions substantially disappear from a tread surface of the tire to be retreaded.
A tire grinding device pertaining to a fourth aspect of the present invention includes: a holding mechanism that rotatably holds a tire to be retreaded about a device axial center and causes the tire to be retreaded to rotate about the device axial center; grinding means that contacts a tread portion of the tire to be retreaded that is rotated by the holding mechanism and grinds the tread portion; a metal detection sensor that detects, along a rotating direction whose center is the device axial center, a distance from the device axial center to a metal belt layer of the tire to be retreaded that is held by the holding mechanism; and grinding position adjusting means that causes, when the tire to be retreaded is grinded by the grinding means, the grinding means to relatively move with respect to the tire to be retreaded along a radial direction whose center is the device axial center on the basis of a position along a rotating direction of the tire to be retreaded and the detected value of the distance from the device axial center to the belt layer.
In the tire grinding device pertaining to a fourth aspect, first, the distance from the device axial center to the metal belt layer of the tire to be retreaded that is held by the holding mechanism is detected by the metal detection sensor along the tire rotating direction, whereby the distance from the device axial center to the belt layer that corresponds to the position (phase) along the rotating direction of the tire to be retreaded can be determined as a detected value by a detection signal of the metal detection sensor, so the eccentricity amount and the eccentricity direction of the tire to be retreaded with respect to the device axial center that correspond to the phase of the tire to be retreaded can be respectively determined on the basis of this detected value.
In the tire grinding device pertaining to a fourth aspect, next, the grinding means is caused to relatively move with respect to the tire to be retreaded along the radial direction whose center is the device axial center on the basis of the phase of the tire to be retreaded and the eccentricity amount and eccentricity direction of the tire to be retreaded that have been determined as described above, and the tread portion of the tire to be retreaded that is rotated by the holding mechanism is grinded by the grinding means, whereby the tire to be retreaded can be grinded by the grinding means such that the thickness of residual rubber on the outer peripheral side of the belt layer of the tire to be retreaded becomes constant even when eccentricity with respect to the device axial center arises in the tire to be retreaded.
Further, in a tire grinding device of a fifth aspect in the tire grinding device of a fourth aspect, the grinding position adjusting means causes, when the tire to be retreaded is grinded by the grinding means, the grinding means to relatively move with respect to the tire to be retreaded along the radial direction, such that a distance from a center of curvature of the belt layer to the grinding means becomes constant, on the basis of the position along the rotating direction of the tire to be retreaded and the detected value of the distance from the device axial center to the belt layer that has been detected by the metal detection sensor.
As described above, according to the tire grinding method and grinding device pertaining to the present invention, a tire to be retreaded can be grinded by grinding means such that the thickness of residual rubber on an outer peripheral side of a belt layer of the tire to be retreaded becomes constant even when eccentricity with respect to a device axial center arises in the tire to be retreaded.